- Before building Index object (IMDIndex), we build LogicalIndexes
  via calling `gpdb::Plgidx(oidRel)` in which a partition tables is
  traversed and index  information (such as logicalIndexOid,
  nColumns, indexKeys, indPred, indExprs, indIsUnique, partCons,
  defaultLevels) is captured.
- For Indexes which are available on all the partitions partCons
  and defaultLevels are NULL/empty.
- Later in `CTranslatorRelcacheToDXL::PmdindexPartTable` to build
  Index object, we use the derived LogicalIndexes information and
  populates the array  holding the levels on which default
  partitions exists. But since defaultLevels is NIL in this case,
  pdrgpulDefaultLevels is set to empty i,e `default partitions on levels: {}`
- This causes an issue while trying to build the propagation expression,
  as because of wrong number of default partitions on level we mark the
  scan as partial and tries to construct a test propagation expression
  instead of a const propagation expression.
- This patch fixes the issue by marking the default partitions on
  levels for index equal to the default partitions on levels for the
  part relation if the index exists on all the parts.
Signed-off-by: NJemish Patel <jpatel@pivotal.io>